If you’re using any recent release of iOS or iPadOS, be it 13 or 14, then your handset automatically attempts to protect your hearing by reducing loud sounds when using headphones for extended periods of time.
The option to reduce loud sounds is adjustable in the Settings app, but as many users have pointed out on Apple’s support forums, the adjustment has its limits and may still negatively impact the media consumption experience in certain scenarios even when the user takes steps to mitigate interruptions.